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The sensors work by detecting extremely low-frequency electrical activity over a distance of 5 microns (one micron being equal to one millionth of a metre). This microscopic scale and sensitivity allows the sensor to map a high-resolution image of electrical charge that occurs over the surface of a source material (for example a human finger), when it makes contact with a thin insulating surface (ie a plastic surface). The trace of this electrical charge left behind in the fingerprint is imaged using an electric field microscopy system.

In addition to testing the system to detect fingerprints, the research team did a series of experiments in which they tested the same fingerprint on the same surface every day for 14 days. They determined that the fingerprint’s electrical activity decays over time. This leads to the possibility that fingerprints might be able to be dated — thereby ruling out suspects if their fingerprints are too old to have been left at the time of the crime.

There are a few caveats here, though. It appears that different materials have different decay rates – so for this to be used in the field, I’m guessing that a pretty big database of materials will have to be built up before age detection becomes reliable. Moreover, it’s not clear how other factors might impact this. I’d be curious to see if, for example, the fingerprints of smokers or drug users might decay differently, since their chemical residues can actually be found in fingerprints.

The technique also doesn’t work on conducting materials, such as metals, since the electric charge on those surfaces will dissipate.

That said, even if the fingerprint age problems becomes too difficult to tackle in the near future, this technique seems to hold promise on its own as a detection technique that can be employed fairly quickly. Even better, the technique is non-destructive, meaning that other analyses of the fingerprints can be performed after it has been used.

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